A gas-chromatography mass-spectrometry (GC/MS) technique may be used for analyzing gas mixtures. In such an application, the gas chromatography (GC) column separates sample components from the sample gas mixture and the separated components are chemically analyzed in the mass spectrometer.
The application of the GC/MS technique to trace vapor detection and analysis imposes stringent requirements on the acquisition and introduction of the sample to the trace vapor detector. Gas chromatography requires the introduction of a sample in a concentrated pulse. The distribution of trace vapor in the sampling environment of ambient air, however, is extremely diffuse. Although fast gas chromatography employing a capillary column is available for separating sample components on the order of about ten seconds, limitations in commercially available equipment, especially the sample inlet system, have prevented general application of high-speed gas chromatography. In particular, traditional methods of accumulating a trace vapor sample with the proper pulse concentration for delivery to the GC column are too slow for realistic application in trace vapor detection.
One method to improve the inlet system is the use of a vapor collection cold trap as the inlet device. After accumulation of the trace vapor sample in the cold trap, the inlet device is heated to input quickly the collected sample to the GC column. See, e.g., R. F. Mouradian et al., Evaluation of a Nitrogen-Cooled, Electrically Heated Cold Trap Inlet for High-Speed Gas Chromatography, 28 J. CHROMATOGRAPIC SCIENCE 643-48 (Dec. 1990).
To achieve a practical GC/MS trace vapor detection system, the accumulation and delivery of the trace vapor sample to the GC column and the separation and analysis of the sample must occur in real time, i.e., in a matter of minutes or preferably seconds. However, even with the development of the cold trap inlet system, the GC/MS methodology has not been adapted for general application in trace vapor analysis and detection. Furthermore, existing methods of directing the sample flow through a collection device such as the cold trap and through the GC column to the mass spectrometer do not make full use of the speed of the individual instrument components to facilitate flow distribution and achieve real time trace vapor detection.